1. Field of the Invention
This invention relates to an etching method of organic insulating films, and particularly to an etching method suitable for etching organic insulating films used in the production of semiconductor devices.
2. Description of the Related Art
[Prior Art 1]
As a method for etching an organic insulating film while preventing the microtrenching without using etch stop layer, for example, the method of WO 01/15213 A1 (JP-A-2001-60582) is known. The gazette of the above-mentioned patent gives the following description.
Thus, the wafer temperature is maintained at 20–60° C., in accordance with the processing. Then, a gaseous mixture of N2, H2 and Ar is introduced into the processing chamber. The inner pressure of the processing chamber is adjusted to 500 mTorr or more substantially, and preferably 500–800 mTorr substantially. Then, a radio-frequency voltage having a frequency of 13.56 MHz and a power of 600–1,400 W is applied to the lower electrode, and a radio-frequency power having a frequency of 60 MHz and a power of 600–1,400 W is applied to the upper electrode. By taking such a measure, a high-density plasma is generated in the processing chamber and, due to the plasma, contact holes of a desired shape are formed in the insulating layer between layers of wafer made of an organic low-dielectric constant material.
Further, the same gazette as above makes the following mention, too.
A treating gas containing at least a nitrogen atom-containing gas and a hydrogen atom-containing gas is introduced into the processing chamber, and the inner pressure of the vacuum processing chamber is adjusted substantially to 500 mTorr or more to carry out etching of the organic layer film formed on the wafer to be etched placed in the processing chamber. As the material constituting the organic film, a low-dielectric constant material having a relative permittivity of 3.5 or less is preferable. The inner pressure of the vacuum processing chamber is preferably kept at 500–800 mTorr substantially.
By using a gas containing at least a nitrogen atom-containing gas and a hydrogen atom-containing gas as the processing gas and adjusting the inner pressure of the vacuum processing chamber substantially to 500 mTorr or higher, microtrenching can be prevented without using etch stop layer and the mask-selection ratio can be enhanced. Such a technique is especially effective for processes which require to stop the etching in the midst of an organic layer film, such as the dual damascene process, or the like.
It is possible to use N2 as the nitrogen atom-containing gas or to use H2 as the hydrogen atom-containing gas, if desired. In the gazette referred to above, there are mentioned some examples in which the N2/H2 flow rate ratio (N2/H2) is 400 sccm/400 sccm, 200 sccm/200 sccm, and 100 sccm/300 sccm.
[Prior Art 2]
As another method for etching an organic insulating film, the method of JP-A-2000-252359 is known. The following description is given in the gazette thereof.
An insulating film (insulating film) between layers made of an organic dielectric film such as polyallyl ether is subjected to etching, while forming a CN group-containing reaction product, etc. by the use of an NH group-containing ion or radical generated from a gas plasma made from a mixture of hydrogen and nitrogen or an ammonia-containing gas.
The etching process of the insulating film between layers is carried out by means of ECR type (Electron Cyclotron Resonance type) plasma etching apparatus under conditions of, for example, a substrate-provided electrode temperature of 20° C., a μ-wave power (2.45 GHz) of 2,000W, a pressure of 0.8 Pa, an RF power of 300 W, by using NH3 as an etching gas at a flow rate of 100 sccm.
In the etching process mentioned above, it is also possible, if desired, to carry out the etching process by the use of a gas plasma comprising a gaseous mixture of hydrogen and nitrogen at a flow rate (N2+H2) of, for example, 100 sccm at a H2/N2 flow rate ratio of, for example, 75/25 sccm.
By carrying out the etching using NH group-containing ion or radical, an insulating film containing an organic dielectric film can be subjected to an anisotropic etching without forming a damage layer causing defective conduction, while suppressing side etching, while maintaining a high etch rate of about 450 nm/minute, without bringing about a reduction of throughput, and rapidly.
By such a technique, it is also possible to etch an insulating film containing an organic insulating film to open contact holes. This technique is applicable also to an etching process for forming trench for interconnect wiring such as damascene process, or to an etching process for simultaneously opening trench for interconnect wiring and contact hole such as dual damascene process, etc.
Further, if etching process of insulating film between layers is carried out under various conditions [(a) N2=100 sccm, (b) N2/H2=50/50 sccm and (c) H2=100 sccm] and emission spectra are measured, an NH peak observable neither in the case (a) using N2 gas nor in the case (c) using H2 gas is observed in the case (b) using N2/H2 mixture. Further, as for CN peak, the peak intensity observed in the case (b) using N2/H2 mixture is higher than the peak intensity in the case (a) using N2 gas and in the case (c) using H2 gas.
Further, if the flow rate ratio of etching gas is so varied that N2/H2=100/0 to 50/50 to 0/100 sccm and the relative etch rate (the etch rate at N2/H2=100/0 sccm is taken as 1) and the emission spectral intensity ratios between the light-emitting components (CN, NH, N2, CH, H) at varied flow rate ratios are measured, it is found that the etch rate and the emission spectral intensity ratio between CN and NH are roughly the same in the behavior.